Data path for multi-level cell memory, methods for storing and methods for utilizing a memory array

ABSTRACT

Memories, data paths, methods for storing, and methods for utilizing are disclosed, including a data path for a memory using multi-level memory cells to provide storage of multiple bits per memory cell. One such data path includes a bit mapping circuit and a data converter circuit. Such a bit mapping circuit can be configured to map bits of the original data to an intermediate arrangement of bits and such a data converter circuit can be configured to receive the intermediate arrangement of bits and convert the intermediate arrangement of bits into intermediate data corresponding to a memory state to be stored by memory cells of a memory cell array.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of pending U.S. patent applicationSer. No. 12/261,928, filed on Oct. 30, 2008, which application isincorporated herein by reference, in its entirety, for any purpose.

TECHNICAL FIELD

Embodiments of the present invention relate generally to semiconductormemory and specifically, in one or more of the illustrated embodiments,to semiconductor memory having a data path for storing more than onebinary digit of digital information per memory cell.

BACKGROUND OF THE INVENTION

Each memory cell of a semiconductor memory system, such as a memorydevice, has traditionally been used to store one binary digit (“bit”) ofdigital information. In order to store large amounts of digitalinformation large arrays of memory cells are used. One challenge that ispresented by the traditional approach of one bit per cell is tocontinually shrink the size of the memory array in order to increase thecapacity of the memory without dramatically increasing the overall sizeof the memory system. Example approaches to reduce the size of the arrayhave been to design memory cells that occupy less area and reducing thedistance between the memory cells in order to increase memory celldensity and capacity. As the feature size of the memory cells becomessmaller, however, the complexity of fabricating the memory increasesresulting in increased cost of manufacturing.

A relatively recent approach to increasing memory capacity has been todesign memory cells and supporting circuitry for storing multiple bitsof digital information in each memory cell. For example, rather thanstore one bit of digital information, as has been the tradition, twobits of digital information are stored by a memory cell. Storage of twobits of digital information is accomplished by having memory cells andread/write circuitry that can accurately store, read, and write fourdistinct memory states. Each of the four memory states represents adifferent combination of two bits of information, that is, 00, 01, 10,and 11. In contrast, the traditional one bit per cell approach requiresmemory cells and read/write circuitry that can accurately store, read,and write two distinct memory states, each distinct memory staterepresenting either a 0 or 1. Use of memory cells for storing more thantwo memory states may be applicable for different types of memory, forexample, in both volatile (e.g., DRAM) and non-volatile memory (e.g.,flash memory).

Projecting forward along the current trajectory of using memory cellsfor storing more than two memory states, starting with using twodifferent memory states for storing one bit of digital information andevolving to using four different memory states for storing two bits ofdigital information, three bits of digital information may be stored byusing eight different memory states and four bits of digital informationmay be stored by using sixteen different memory states. As illustratedby this example, the number of memory states per memory cell is apower-of-two, and the resulting number of bits stored per cell is thebase two logarithm of the number of memory states.

A challenge with designing memory systems along this trajectory is thedifficulty of reliably and accurately storing, reading, and writing, forexample, twice as many memory states as the previous iteration. Evolvingfrom storing, reading and writing two memory states to storing, readingand writing four memory states presented difficulties that wereeventually overcome. Evolving from using four memory states to usingeight memory states, however, presents challenges that are much moredifficult with the current state of technology than those presented inthe previous evolution of two memory states to four memory states.Although the difficulties are not insurmountable and will eventually beovercome, it is desirable to have, for example, memory systems utilizingmemory cells for storing multiple memory states to provide a storagedensity of greater than one bit per cell without being limited tostoring a power-of-two number of memory states.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a data path according to an embodiment ofthe present invention.

FIG. 2A is a block diagram of a data path having a bit mapping and dataconversion circuit 130 according to an embodiment of the presentinvention. FIG. 2B is a table of resulting bit/cell storage densitiesrelated to using pairs of multi-level memory cells of a memory arrayhaving non-power-of-two number of memory states.

FIG. 3 are truth tables for storing binary user data using pairs ofmulti-level memory cells having six memory states according to anembodiment of the invention.

FIG. 4 are truth tables for storing binary user data using pairs ofmulti-level memory cells having three memory states according to anembodiment of the invention.

FIG. 5 is a block diagram of a data path according to an embodiment ofthe present invention for storing data using pairs of multi-level memorycells having six memory states.

FIG. 6 is a block diagram of a data path according to another embodimentof the present invention for storing data using pairs of multi-levelmemory cells having three memory states.

FIG. 7 is a block diagram of a data path according to another embodimentof the present invention for storing data using pairs of multi-levelmemory cells having four memory states.

FIG. 8 is a block diagram of a memory system having a data pathaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficientunderstanding of embodiments of the invention. However, it will be clearto one skilled in the art that embodiments of the invention may bepracticed without these particular details. Moreover, the particularembodiments of the present invention described herein are provided byway of example and should not be used to limit the scope of theinvention to these particular embodiments. In other instances,well-known circuits, control signals, timing protocols, and softwareoperations have not been shown in detail in order to avoid unnecessarilyobscuring the invention.

FIG. 1 illustrates a data path 100 according to an embodiment of thepresent invention. The data path 100 couples data applied toinput/output (I/O) nodes, such as terminals 106 to a flash memory array120 to write data and couples data from the flash memory array 120 tothe I/O terminals 106 to provide read data. The memory array 120includes multi-level memory cells that store P different memory cellstates, where P can be a non-power-of-two number. The data path 100includes an I/O latch 110 coupled to I/O terminals 106 to latch binarydigits (i.e., “bits”) of information. In the embodiment illustrated inFIG. 1, the I/O latch 106 is 8-bits wide, and the I/O terminals 106represent eight I/O terminals. A bit mapping and data conversion circuit130 according to an embodiment of the present invention is coupled tothe latch 110. The bit mapping and data conversion circuit 130, as willbe described in more detail below, is configured to enable the memoryarray 120 to store N bits/cell, where N can be a non-integer number. Thebit mapping and data conversion circuit 130 is coupled through a databus 136 (shown in FIG. 1 as 8-bits wide) to a page buffer 134, which isin turn coupled to sense amplifiers 138 and the flash memory array 120.The data path 100 is similar to a conventional data path, except forincluding a bit mapping and data conversion circuit coupled between theI/O latch 110 and the buffer 134. In the embodiment illustrated in FIG.1, the page buffer can store 4 kBits (4,096 bits) and the senseamplifiers 138 include 4 k sense amplifiers. The particularbit-dimensions provided for the data path 100 are provided by way ofexample, and other embodiments of the invention include componentshaving different bit-dimensions.

FIG. 2A illustrates the data path 100 having a bit mapping and dataconversion circuit 130 according to an embodiment of the invention. Thebit mapping and data conversion circuit 130 includes a bit mappingcircuit 210 coupled through a bus 214 to a register 220 for mapping bitsof data from the I/O latch 110 to the register 220, and vice versa. Adata converter 230 coupled to the register 220 through bus 224 convertsdata bits into intermediate binary data (IBD) that is provided over bus234 to be written to the page buffer 134 through a multiplexer 240. Thedata converter 230 further converts IBD read from the page buffer 134into data to be stored in the register 220 to then be provided throughthe bit mapping circuit 210 to the latch 110. The multiplexer 240 routesthe IBD between the bus 234 and the bus 136, which may have differentbit-widths. In the embodiment of the invention illustrated in FIG. 2A,the I/O latch is 8-bits wide, and the bus 136 is also 8-bits wide.However, in other embodiments, the bit-widths of the busses can bedifferent.

In operation, the bit mapping and data conversion circuit 130 can beconfigured to convert binary user data to IBD, and vice versa. The IBDis intermediate binary data that can be stored as a memory cell state ina memory cell of the memory array 120. As previously mentioned, the bitmapping and data conversion circuit 130 can be used to enable binaryuser data to be stored using groups of multi-level memory cells capableof storing non-power-of-two memory states to effectively store anon-integer number of bits-per-cell. The storage of binary user datausing groups of memory cells having non-power-of-two states to provide anon-integer number of bits-per-cell is transparent to a user, who canwrite and read binary data in conventional byte and word lengths.

Examples of different configurations of the bit mapping and dataconversion circuit 130 are shown in table 250 of FIG. 2B, which areprovided as non-limiting examples. The example configurations shown intable 250 result from utilizing groups of two memory cells and provide arespective bits-per-cell storage density for the corresponding number ofmemory states storable by memory cells in the array. For example,assuming groups of two memory cells, the bit mapping and data conversioncircuit 130 can be configured to provide a storage density of 2.5bits/cell when used with memory cells having six storable memory states.In another configuration, the bit mapping and data conversion circuit130 can provide a storage density of 2 bits/cell when used with memorycells having four storable memory states. As illustrated by the latterexample, the bit mapping and data conversion circuit 130 can also beused with memory cells having typical power-of-two storable memorystates to provide typical bits-per-cell storage densities.

FIG. 3 illustrates tables 310 and 320 for converting between binary userdata and IBD stored by groups of two memory cells, each having sixmemory states, according to an embodiment of the invention. Aspreviously discussed with reference to FIG. 2 and table 250, in anembodiment utilizing memory cells having six storable memory states(L0-L5) and using a group of two memory cells (Cell0 and Cell1), astorage density of 2.5 bits/cell is achieved. Table 310 illustratesassignment of combinations of the six memory states (L0-L5) of the twomemory cells to 5-bit values of binary user data. As will be describedin more detail below, a user's 8-bit data (i.e., 1 byte) is divided into5-bit binary data that is converted into IBD by the data converter 230.The IBD is then stored in a pair of memory cells. Table 320 illustratesthe conversion between the IBD and the memory states for the individualcells of the pair.

For example, where the 8-bit binary user data is 01011101 (B7:B0) and isto be written to memory, the user data is split into first 5-bit binarydata, with the remaining 3-bits to be part of another 5-bit binary data.In the particular example, the first 5-bit binary data (B4:B0) is 11101and the remaining 3-bits 010 (B7:B5) will be joined with five other bitsfrom other 8-bit binary user data. Turning to the 5-bit binary data11101 (B4:B0) and table 310, the binary data corresponds to acombination of memory cell states L0 and L2 stored by a pair ofmultilevel memory cells Cell0 and Cell1, respectively. As will bedescribed in more detail below, in determining the memory state to bestored by the respective memory cell, the 5-bit binary data is convertedinto two 3-bit IBDs, which are each in turn stored as a correspondingmemory state in a respective memory cell according to table 320.

In reading data from memory, a pair of cells are accessed and therespective memory states are conventionally sensed for memory cellshaving six memory states to provide corresponding 3-bit IBDs for eachmemory cell. For example, reading memory cell states L0 and L2 stored bymemory cells Cell0 and Cell1, respectively, the two memory cells areaccessed and memory states L0 and L2 result in two 3-bit IBDs of 111 and101. The 3-bit IBDs are converted back into 5-bit binary data. Accordingto table 310, the resulting 5-bit data is 11101, which is the original5-bit binary data from the previous example of writing data to memory.The 5-bit binary data is then concatenated to other 5-bit binary dataread from the memory and split into the original 8-bit binary user data.

FIG. 4 illustrates tables 330 and 340 for converting between binary userdata and IBDs stored by groups of two memory cells, each having threememory states, according to an embodiment of the invention. Aspreviously discussed with reference to FIG. 2 and table 250, in anembodiment utilizing memory cells having three storable memory states(L0-L2) and using a group of two memory cells (Cell0 and Cell1), astorage density of 1.5 bits/cell is achieved. Table 330 illustratesassignment of combinations of the three memory states (L0-L2) of the twomemory cells to 3-bit values of binary user data. As will be describedin more detail below, a user's 8-bit data is divided into 3-bit binarydata that is converted into IBD by the data converter 230. The IBD isthen stored in a pair of memory cells. Table 340 illustrates theconversion between the IBD and the memory states for the individualcells of the pair.

For example, where the 8-bit binary user data is 01011101 (B7:B0) and isto be written to memory, the user data is split into first and second3-bit binary data (B2:B0) and (B5:B3), with the remaining 2-bits (B7:B6)to be part of another 3-bit binary data. In the particular example, thefirst 3-bit binary data is 101, the second 3-bit binary data is 011, andthe remaining 2-bits 01 will be joined with one other bit from other8-bit binary user data. Turning to the two 3-bit binary data 101 and011, and table 330, the first binary data 101 corresponds to acombination of memory cell states L1 and L0 stored by a first pair ofmultilevel memory cells Cell0 and Cell1, respectively. The second binarydata 011 corresponds to a combination of memory cell states L1 and L2stored by a second pair of multilevel memory cells Cell0 and Cell1,respectively. As will be described in more detail below, in determiningthe memory state to be stored by the respective memory cell, the 3-bitbinary data is converted into two 2-bit IBDs, which are each in turnstored as a corresponding memory state in a respective memory cell.

In reading data from memory, a pair of cells are accessed and therespective memory states are conventionally sensed for memory cellshaving three memory states to provide corresponding 2-bit IBDs for eachmemory cell. For example, taking memory cell states L1 and L0 stored bythe first pair of memory cells Cell0 and Cell1, respectively, the twomemory cells are accessed and memory states L1 and L0 result in two IBDsof 10 and 11. Memory cell states L1 and L2 stored by a second pair ofmultilevel memory cells Cell0 and Cell1, respectively, the two memorycells are accessed and memory states L1 and L2 result in two IBDs of 10and 01. The 2-bit IBDs are converted back into 3-bit binary data. In thepresent example, the resulting 3-bit binary data for the first pair ofmemory cells is 101 and the resulting 3-bit binary data for the secondpair of memory cells is 011, in accordance with table 330, which are theoriginal 3-bit data from the previous example of writing data to memory.The 3-bit binary data is then concatenated to other 3-bit binary dataread from the memory and split into the original 8-bit binary user data.

FIG. 5 illustrates the data path 100 having a bit mapping and dataconversion circuit 130 according to an embodiment of the presentinvention. The data path 100 of FIG. 5 can be used to implement the sixmemory state, two cell example previously discussed with reference toFIG. 3. The embodiment of the invention shown in FIG. 5 includes an8-bit input/output latch coupled through a bit mapping circuit 210 to a48-bit register 220. The 48-bit register 220 provides binary data toeight data converter subcircuits 230A-H that convert the binary userdata into IBDs, which are written to a multi-level memory cell arraythrough multiplexers 240, data bus 136 and a buffer 134. Senseamplifiers 138 convert between memory states stored by the multi-levelmemory cells and IBDs stored in the page buffer 134.

In operation, 8-bit user data loaded in the latch 110 is sequentiallyprovided to the bit mapping circuit 210 to have the bits of the userdata mapped to corresponding locations of the register 220. In theembodiment shown in FIG. 5, the 8-bit user data is mapped through thebit mapping circuit 210 until the appropriate number of bits of userdata are loaded into the register 220. In the present example of sixmemory states and two cells, the 8-bit user data is split into 5-bitbinary data, as previously discussed. The 5-bit binary data stored inthe register 220 are provided to data converter subcircuits 230A-H to beconverted into pairs of 3-bit IBDs, which are in turn converted intomemory states stored in respective memory cells.

For example, using the previously described example with reference toFIG. 3, 8-bit binary user data 01011101 (B7:B0) is loaded into the latch110 to be mapped through bit mapping circuit 210 into register 220. Inthe embodiment shown in FIG. 5, bits 11101 (B4:B0) would be mapped tofive of six bit register locations of the register 220 that are coupledto data converter subcircuit 230A and bits 010 (B7:B5) would be mappedto three of six bit register locations of the register 220 that arecoupled to data converter subcircuit 230B. 8-bit binary user datacontinues to be loaded through the bit mapping circuit 210 until theregister 220 is loaded. In the example of splitting the 8-bit user datainto 5-bit binary data, five 8-bit bytes of user data can be loaded inthe 48-bit register 220 until the its capacity is reached. The dataconverter subcircuits 230A-H convert the 5-bit binary data into 3-bitIBDs, as previously discussed. With reference to table 310 of FIG. 3,the 5-bit data 11101 of the particular example is converted by dataconverter subcircuit 230A into 3-bit IBDs 111 and 101, which areprovided over bus 234 to be loaded bit-by-bit through multiplexer 240and data bus 136 to locations 134A and 134B in the page buffer 134. Theother 5-bit binary data stored in the register 220 are similarlyconverted into respective pairs of 3-bit IBDs by the data convertersubcircuits 230B-H and loaded through the bus 234, mutliplexer 240, anddata bus 136 into the page buffer 134.

After the page buffer 134 is loaded with the IBDs, sense amplifiers 138convert the respective 3-bit IBD into a corresponding memory state to bestored in a respective multi-level memory cell. Sense amplifiers forconverting the IBDs into a corresponding memory state is known in theart, and sense amplifiers of conventional design can be used for thesense amplifiers 138. In the present example, the 3-bit IBD 111corresponds to memory state L0 (with reference to table 320 of FIG. 3)and is stored in a first memory cell Cell0 of a pair of memory cellsCell0, Cell1 (not shown) used to store the 5-bit binary data. The 3-bitIBD 101 corresponds to L2 and is stored in a second memory cell Cell1.

When reading data from the multi-level memory cells, the process ofwriting data to the multi-level memory cells is generally reversed. Thatis, the memory states stored by multi-level memory cells are sensed bysense amplifiers 138 and converted into 3-bit IBDs that are stored inrespective locations in the page buffer 134. The IBDs from pairs ofmemory cells are coupled to the respective data converter subcircuit,for example, IBDs stored by locations 134A, 134B are coupled through thedata bus 136, multiplexers 240 and bus 234 to the data convertersubcircuit 230A. The two 3-bit IBDs are converted by the data converters230 into corresponding 5-bit binary data that is stored in appropriatebit locations in register 220. The bit mapping circuit 210 maps the5-bit binary data into 8-bit data to reconstruct the original 8-bitbinary user data.

FIG. 6 illustrates the data path 100 previously described with referenceto FIG. 5 having the bit mapping and data conversion circuit 130configured implement the three memory state, two cell example previouslydiscussed with reference to FIG. 4. That is, in some embodiments of theinvention, the data path 100 can be configured to implement differentbit/cell storage densities in a memory having multi-level memory cells,including multi-level memory cells capable of storing non-power-of-twomemory states and bit/cell storage densities that are non-integernumbers.

In operation, 8-bit binary user data loaded in the latch 110 issequentially provided to the bit mapping circuit 210 to have the bits ofthe user data mapped to corresponding locations of the register 220. Inthe embodiment shown in FIG. 6, the 8-bit user data is mapped throughthe bit mapping circuit 210 into 3-bit binary data, as previouslydiscussed with reference to FIG. 4, which are stored in the register220. The 3-bit binary data stored in the register 220 are provided todata converter subcircuits 230A-H to be converted into pairs of 2-bitIBDs, which are in turn converted into memory states stored inrespective memory cells.

For example, using the previously described example with reference toFIG. 4, 8-bit binary user data 01011101 (B7:B0) is loaded into the latch110 to be mapped through bit mapping circuit 210 into register 220. Inthe embodiment shown in FIG. 6, bits 101 (first 3-bits B2:B0) are mappedto three of six bit register locations coupled to data convertersubcircuit 230A and bits 011 (second 3-bits B5:B3) are mapped to threeof six bit register locations coupled to data converter subcircuit 230B.The remaining bits 01 (B7:B6) are mapped to two of six bits registerlocations coupled to data converter subcircuit 230C, which will beconcatenated to 1-bit of the next 8-bit user data loaded into the latch110. 8-bit binary user data continues to be loaded through the bitmapping circuit 210 until the register 220 is loaded. In the example ofsplitting the 8-bit user data into 3-bit binary data, three 8-bit bytesof user data can be loaded in the 48-bit register 220 until the itscapacity is reached. The data converter subcircuits 230A-H convert the3-bit binary data into 2-bit IBDs, as previously discussed withreference to table 340 of FIG. 4. The first 3-bit data 101 is convertedby data converter subcircuit 230A into 2-bit IBDs 10 and 11, which areprovided over bus 234 to be loaded bit-by-bit through multiplexer 240and data bus 136 to locations 134A and 134B in the page buffer 134. Thesecond 3-bit data 011 is converted by data converter subcircuit 230Binto 2-bit IBDs 10 and 01, which are provided over bus 234 to be loadedbit-by-bit through multiplexer 240 and data bus 136 to locations 134Cand 134D in the page buffer 134.

When reading data from the multi-level memory cells, the memory statesstored by multi-level memory cells are sensed by sense amplifiers 138and converted into 2-bit IBDs that are stored in respective locations inthe page buffer 134. The IBDs from pairs of memory cells are coupled tothe respective data converter subcircuit, for example, IBDs stored bylocations 134A, 134B and IBDs stored by locations 134C, 134D are coupledthrough the data bus 136, multiplexers 240 and bus 234 to the dataconverter subcircuit 230A and 230B, respectively. The pairs of 2-bitIBDs are converted into corresponding 3-bit binary data, which arestored in appropriate bit locations in register 220. The bit mappingcircuit 210 maps the 3-bit binary data into 8-bit data to reconstructthe original 8-bit user data.

FIG. 7 illustrates the data path 100 previously described with referenceto FIG. 5 having the bit mapping and data conversion circuit 130configured implement a four memory state, two cell example to provide abit/cell storage density of 2 bits/cell. As previously described withreference to FIGS. 5 and 6, the data 100 can be used for memories havingmulti-level memory cells capable of storing non-power-of-two memorystates to provide bit/cell storage densities that are non-integernumbers. As shown in the embodiment of FIG. 7, the data conversioncircuit 130 can also be configured to work with multi-level memory cellscapable of storing power-of-two memory states to provide an integernumber of bit/cell storage density. Operation of the embodimentillustrated in FIG. 7 is similar to that previously described withreference to FIGS. 5 and 6. In summary, the 8-bit user data is splitinto 4-bit binary data mapped to four of six bit register locationscoupled to a respective data converter subcircuit 230. The 4-bit binarydata is converted by the respective data converter subcircuit into two2-bit IBDs. Each of the 2-bit IBDs are provided to the page buffer 134and converted by the sense amplifiers 138 into a corresponding memorystate to be stored in the memory array. Reading data is essentially thereverse of writing data to the memory array.

A truth table for the mapping of binary user data and conversion toIBDs, and then to corresponding memory states for the four memory state,two memory cell example of FIG. 7, has not been provided herein, in theinterest of brevity because such truth tables can be conventional. Forexample, each of the four memory states can correspond to a different2-bit IBD (00, 01, 10, 11). Using a pair of memory cells, each memorycell having four memory states, sixteen different 4-bit combinations canbe made. Each of the different 16-bit combinations can be represented bya different combination two 2-bit IBDs. As previously discussed, theresulting storage density is 2 bits/cell.

One or more Embodiments of the present invention can also have a bitmapping and data conversion circuit 130 configurable for use withdifferent combinations of memory states to provide different bit/cellstorage densities. In one embodiment, configuration of such a bitmapping and data conversion circuit can be reconfigured by user. Forexample, with reference to FIGS. 2A and 2B, given an N bits/cell storagedensity, a user can select N on a block boundary of the memory array,and configures the bit-widths of the bus 214 coupled between the bitmapping circuit 210 and the register 220, bus 224 coupled between theregister 220 and the data converter 230, and bus 234 coupled between thedata converter 230 and the multiplexer 240 to provide the desired Nbits/cell. In still other embodiments of the invention, the bit mappingand data conversion circuit does not need to be configurable.

The specific embodiments previously described have been provided by wayof example, and is not intended to limit the scope of the presentinvention. Modifications can be made to the previous embodiment andremain within the scope of the present invention. For example, in otherembodiments of the invention, the bit mapping and data conversioncircuit 130 can include registers having greater or lesser bit capacitythat than described with reference to FIG. 5. Additionally, the couplingof data converters to bit register locations and the bit-widths of thebuses may be different in other embodiments as well. Therefore, thoseordinarily skilled in the art will understand the previously describedembodiments are not intended to limit the scope of the presentinvention.

FIG. 8 illustrates a memory system 400 that includes a data pathaccording an embodiment of the invention. The memory system 400 includesan array 430 of memory cells arranged in banks of rows and columns. Inone embodiment, the memory cells of the array 430 are non-volatilememory. In some embodiments, the non-volatile memory cells are capableof storing multiple memory states, including non-volatile memory cellscapable of storing a non-power-of-two number of memory states.

Most command signals, the address signals and the write data signals areapplied to the memory system 400 as sets of sequential input/output(“I/O”) signals transmitted through an I/O bus 434. The I/O bus 134illustrated in FIG. 8 may include I/O terminals 106 and I/O latch 110(not shown in FIG. 8). Similarly, read data signals are output from thememory system 400 through the I/O bus 434. The I/O bus is connected toan I/O control unit 440 that routes the signals between the I/O bus 434and an internal data bus 442, an internal address bus 444, and aninternal command bus 446. The internal data bus 442 may include a datapath according to an embodiment of the present invention. A bit mappingand data conversion circuit 130 according to an embodiment of thepresent invention is coupled to the internal data bus 442. As previouslydiscussed, the bit mapping and data conversion circuit 130 may be usedto read and write data in multi-level memory cells storing anon-power-of-two number of memory states. The memory system 400 alsoincludes a control logic unit 450 that receives a number of controlsignals either externally or through the command bus 446 to control theoperation of the memory system 400. The address bus 444 applies rowaddress signals to a row decoder 460 and column address signals to acolumn decoder 464. Similarly, the column decoder 464 enables write datasignals to be applied to bit lines for columns corresponding to thecolumn address signals and allow read data signals to be coupled frombit lines for columns corresponding to the column address signals.

In response to the memory commands decoded by the control logic unit450, the memory cells in the array 430 are erased, programmed, or read.The memory array 430 is programmed on a row-by-row or page-by-pagebasis. After the row address signals have been applied to the addressbus 444, the I/O control unit 440 routes write data through the bitmapping and data conversion circuit 130 to a cache register 470. Theintermediate binary data are stored in the cache register 470 inpreparation for programming. The cache register 470 sequentially storesthe sets of intermediate binary data for an entire row or page of memorycells in the array 430. A page buffer (not shown), as previouslydescribed, may be included in or represented by the cache register 470illustrated in FIG. 8. Sense amplifiers previously discussed are notshown in FIG. 8, although those ordinarily skilled in the art understandthe memory system 400 includes sense amplifiers coupled to the memorycells of the array 430. All of the stored intermediate binary data arethen used to program a row or page of memory cells in the array 430selected by the row address coupled through the address bus 444. In asimilar manner, during a read operation, intermediate binary data from arow or page of memory cells selected by the row address coupled throughthe address bus 444 are stored in a data register 480. Sets of theintermediate binary data are then transferred to the bit mapping anddata conversion circuit 130 to provide read data to the I/O control unit440 and then to the I/O bus 434.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A memory, comprising: an array of memory cells, each of the cellsconfigured to store a plurality of memory states; and a bit conversioncircuit coupled to the array of memory cells, the bit conversion circuitconfigured to convert bits of original data into intermediate datacorresponding to a respective memory state.